The present invention relates generally to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat tissue in regions of the spine. The present invention is particularly suited for the treatment of herniated discs and other disorders of intervertebral discs. This invention also relates to treatment of an intervertebral disc by guiding an electrosurgical probe to a target site within an intervertebral disc.
The major causes of persistent, often disabling, back pain are disruption of the disc annulus, chronic inflammation of the disc (e.g., herniation), or relative instability of the vertebral bodies surrounding a given disc, such as the instability that often occurs due to a degenerative disease. Spinal discs mainly function to cushion and tether the vertebrae, providing flexibility and stability to the patient""s spine. Spinal discs comprise a central hydrophilic cushion, the nucleus pulposus, surrounded by a multi-layered ligament, the annulus fibrosus. As discs degenerate, they lose their water content and height, bringing vertebrae closer together. This results in a weakening of the shock absorption properties of the disc and a narrowing of the nerve openings in the sides of the spine which may lead to pinching of the nerve root. This disc degeneration can cause back and leg pain. Weakness in the annulus fibrosus of degenerative discs, or disc injury, can allow fragments of the nucleus pulposus to migrate from within the disc into the annulus fibrosus or the spinal canal. Displaced annulus fibrosus, or protrusion of the nucleus pulposus, e.g., herniation, may impinge on spinal nerves or nerve roots. The mere proximity of the nucleus pulposus or a damaged annulus to a nerve can cause direct pressure against the nerve, resulting in pain and sensory and motor deficit.
Often, inflammation from disc herniation can be treated successfully by non-surgical means, such as rest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosteroids. In some cases, the disc tissue is irreparably damaged, thereby necessitating removal of a portion of the disc or the entire disc to eliminate the source of inflammation and pressure. In more severe cases, the adjacent vertebral bodies must be stabilized following excision of the disc material to avoid recurrence of the disabling back pain. One approach to stabilizing the vertebrae, termed spinal fusion, is to insert an interbody graft or implant into the space vacated by the degenerative disc. In this procedure, a small amount of bone may be grafted and packed into the implants. This allows the bone to grow through and around the implant, fusing the vertebral bodies and preventing reoccurrence of the symptoms.
Until recently, spinal discectomy and fusion procedures resulted in major operations and traumatic dissection of muscle and bone removal or bone fusion. To overcome the disadvantages of traditional traumatic spine surgery, minimally invasive spine surgery was developed. In endoscopic spinal procedures, the spinal canal is not violated and therefore epidural bleeding with ensuring scarring is minimized or completely avoided. In addition, the risk of instability from ligament and bone removal is generally lower in endoscopic procedures than with open discectomy. Further, more rapid rehabilitation facilitates faster recovery and return to work.
Minimally invasive techniques for the treatment of spinal diseases or disorders include chemonucleolysis, laser techniques and mechanical techniques. These procedures generally require the surgeon to form a passage or operating corridor from the external surface of the patient to the spinal disc(s) for passage of surgical instruments, implants and the like. Typically, the formation of this operating corridor requires the removal of soft tissue, muscle or other types of tissue depending on the procedure (i.e., laparascopic, thoracoscopic, arthroscopic, back, etc.). This tissue is usually removed with mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders and the like. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, these instruments might sever blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon""s view of the target site.
Once the operating corridor is established, the nerve root is retracted and a portion or all of the disc is removed with mechanical instruments, such as a pituitary rongeur. In addition to the above problems with mechanical instruments, there are serious concerns because these instruments are not precise, and it is often difficult, during the procedure, to differentiate between the target disc tissue, and other structures within the spine, such as bone, cartilage, ligaments, nerves and non-target tissue. Thus, the surgeon must be extremely careful to minimize damage to the cartilage and bone within the spine, and to avoid damaging nerves, such as the spinal nerves and the dura mater surrounding the spinal cord.
Lasers were initially considered ideal for spine surgery because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, bones, ligaments and spinal nerves often lie within close proximity of the spinal disc, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.
Monopolar and bipolar radiofrequency devices have been used in limited roles in spine surgery, such as to cauterize severed vessels to improve visualization. Monopolar devices, however, suffer from the disadvantage that the electric current will flow through undefined paths in the patient""s body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient""s body. In addition, since the defined path through the patient""s body has a relatively high impedance (because of the large resistance or resistivity of the patient""s body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.
There is a need for an apparatus or system including an electrosurgical instrument, such as a catheter or probe, wherein the instrument can be introduced into an intervertebral disc during an endoscopic procedure, and the distal portion of the instrument can be guided to a target site within the disc, wherein the target site can be treated with minimal or no damage to surrounding, non-target tissue. The instant invention provides such an electrosurgical system and methods for treating tissue by a cool ablation mechanism involving generation of a plasma in the presence of an electrically conductive fluid and molecular dissociation of tissue components, as is described in enabling detail hereinbelow.
The present invention provides systems, apparatus and methods for selectively applying electrical energy to structures within a patient""s body, such as tissue within or around the spine. The systems and methods of the present invention are particularly useful for ablation, resection, aspiration, collagen shrinkage and/or hemostasis of tissue and other body structures in open and endoscopic spine surgery.
In one aspect of the invention, a method is provided for treating discs within a patient""s spine. Specifically, a method of the present invention comprises positioning at least one active electrode within close proximity of a disc in the spine (either endoscopically, or through an open procedure). The dura mater tissue that surrounds the spinal cord is insulated from the active electrode(s) and a high frequency voltage is applied between the active electrode(s) and one or more return electrodes to apply sufficient energy to the disc tissue to reduce the volume of the disc.
In one embodiment, the high frequency voltage is sufficient to ablate at least a portion of the nucleus pulposus, either the extruded portion outside the annulus or a portion or all of the nucleus pulposus within the annulus. In another embodiment, the active electrode is advanced into the annulus and sufficient high frequency voltage is applied to contract or shrink the collagen fibers within the nucleus pulposus. This causes the pulposus to shrink and withdraw from its impingement on the spinal nerve. In other embodiments, the present invention may be used to both ablate the extruded portion of the nucleus pulposus, and then to contract or shrink the inner disc material to allow repair of the annulus.
In a specific configuration, electrically conducting fluid, such as isotonic saline, is directed to the target site between the target disc tissue and the active electrode. In monopolar embodiments, the conductive fluid need only be sufficient to surround the active electrode, and to provide a layer of fluid between the electrode and the tissue. In bipolar embodiments, the conductive fluid preferably generates a current flow path between the active electrode(s) and one or more return electrodes.
In procedures requiring contraction of tissue, high frequency voltage is applied to the active electrode(s) to elevate the temperature of collagen fibers within the tissue at the target site from body temperature (about 37xc2x0 C.) to a tissue temperature in the range of about 45xc2x0 C. to 90xc2x0 C., usually about 60xc2x0 C. to 70xc2x0 C., to substantially irreversibly contract these collagen fibers. In a preferred embodiment, an electrically conductive fluid is provided between the active electrode(s) and one or more return electrodes positioned on an electrosurgical probe proximal to the active electrode(s) to provide a current flow path from the active electrode(s) away from the tissue to the return electrode(s). The current flow path may be generated by directing an electrically conductive fluid along a fluid path past the return electrode and to the target site, or by locating a viscous electrically conducting fluid, such as a gel, at the target site, and submersing the active electrode(s) and the return electrode(s) within the conductive gel. The collagen fibers may be heated either by passing the electric current through the tissue to a selected depth before the current returns to the return electrode(s) and/or by heating the electrically conductive fluid and generating a jet or plume of heated fluid which is directed towards the target tissue. In the latter embodiment, the electric current may not pass into the tissue at all. In both embodiments, the heated fluid and/or the electric current elevates the temperature of the collagen sufficiently to cause hydrothermal shrinkage of the collagen fibers.
In procedures requiring ablation of tissue, the tissue is removed by molecular dissociation or disintegration processes. In these embodiments, the high frequency voltage applied to the active electrode(s) is sufficient to vaporize an electrically conductive fluid (e.g., gel or saline) between the active electrode(s) and the tissue. Within the vaporized fluid an ionized plasma is formed, and charged particles (e.g., electrons) cause the molecular breakdown or disintegration of several cell layers of the tissue. This molecular dissociation is accompanied by the volumetric removal of the tissue. This process can be precisely controlled to effect the volumetric removal of tissue as thin as 10 microns to 150 microns with minimal heating of, or damage to, surrounding or underlying tissue structures. A more complete description of this phenomenon is described in commonly assigned U.S. Pat. No. 5,683,366, the complete disclosure of which is incorporated herein by reference.
In another aspect of the invention, the present invention is useful for performing spinal surgery. The method comprises positioning an electrosurgical instrument in close proximity to an intervertebral disc. An electrically conductive fluid is delivered toward a distal tip of the electrosurgical instrument. A high frequency electrical energy is applied to the active electrode such that the conductive fluid completes a current flow path between the active electrode and a return electrode. The conductive fluid is aspirated through an aspiration lumen positioned proximal of the return electrode. Because the aspiration lumen is positioned away from the fluid delivery lumen and proximal of the return electrode, a plasma can be aggressively created and the tissue can be ablated or contracted more efficiently.
The tissue may be completely ablated in situ with the mechanisms described above, or the tissue may be partially ablated and partially resected and aspirated from this operating corridor. In a preferred configuration, the probe will include one or more aspiration electrode(s) at or near the distal opening of an aspiration lumen. In this embodiment, high frequency voltage is applied between the aspiration electrode(s) and one or more return electrodes (which can be the same or different electrodes from the ones used to ablate tissue) to partially or completely ablate the tissue fragments as they are aspirated into the lumen, thereby preventing clogging of the lumen and expediting the tissue removal process. In other configurations, the aspiration electrodes can be disposed within the aspiration lumen.
The present invention offers a number of advantages over current mechanical and laser techniques for spine surgery. The ability to precisely control the volumetric removal of tissue results in a field of tissue ablation or removal that is very defined, consistent and predictable. The shallow depth of tissue heating also helps to minimize or completely eliminate damage to healthy tissue structures, cartilage, bone and/or spinal nerves that are often adjacent the target tissue. In addition, small blood vessels within the tissue are simultaneously cauterized and sealed as the tissue is removed to continuously maintain hemostasis during the procedure. This increases the surgeon""s field of view, and shortens the length of the procedure. Moreover, since the present invention allows for the use of electrically conductive fluid (contrary to prior art bipolar and monopolar electrosurgery techniques), isotonic saline may be used during the procedure. Saline is the preferred medium for irrigation because it has the same concentration as the body""s fluids and, therefore, is not absorbed into the body as much as certain other fluids.
Apparatus according to the present invention generally include an electrosurgical probe or catheter having a shaft with proximal and distal ends, one or more active electrode(s) at the distal end and one or more connectors coupling the active electrode(s) to a source of high frequency electrical energy. For endoscopic spine surgery, the shaft will typically have a distal end portion sized to fit between adjacent vertebrae in the patient""s spine. In some embodiments, the distal end portion can have an active side which has the active electrodes and an insulated non-active side. In a specific use, the insulator can be used to protect the dura mater (and spinal column) from iatrogenic injury.
Some embodiments of the electrosurgical probe can include a fluid delivery element for delivering electrically conductive fluid to the active electrode(s). The fluid delivery element may be located on the probe, e.g., a fluid lumen or tube, or it may be part of a separate instrument. In an exemplary embodiment, the lumen will extend through a fluid tube exterior to the probe shaft that ends adjacent the distal tip of the shaft. Alternatively, an electrically conducting gel or spray, such as a saline electrolyte or other conductive gel, may be applied to the target site. The electrically conductive fluid will preferably generate a current flow path between the active electrode(s) and one or more return electrodes. In an exemplary embodiment, the return electrode is located on the probe and spaced a sufficient distance from the active electrode(s) to substantially avoid or minimize current shorting therebetween and to shield the return electrode from tissue at the target site.
In a specific configuration, the electrosurgical probe will include an electrically insulating electrode support member having a tissue treatment surface at the distal end of the probe. One or more active electrode(s) are coupled to, or integral with, the electrode support member such that the active electrode(s) are spaced from the return electrode. In one embodiment, the probe includes an electrode array having a plurality of electrically isolated active electrodes embedded in the electrode support member such that the active electrodes extend about 0.2 mm to about 10 mm from the tissue treatment surface of the electrode support member.
In other embodiments, the probe can include one or more lumens for aspirating the electrically conductive fluid from the target area. In an exemplary embodiment, the lumen will extend along the exterior of the probe shaft and end proximal of the return electrode. In a specific configuration, the aspiration lumen and fluid delivery lumen both extend along the exterior of the probe shaft in an annular configuration. The fluid delivery lumen will extend to the distal tip of the shaft while the aspiration lumen will extend only to a point proximal of the return electrode.
In yet another aspect, the present invention provides a method of treating an intervertebral disc having a nucleus pulposus and an annulus fibrosus. The method comprises advancing a distal end of an electrosurgical instrument into the annulus fibrosus. The distal end of the electrosurgical instrument is moved, typically biased or steered, to a curved configuration that approximates a curvature of an inner surface of the annulus fibrosus. A high frequency voltage is delivered between an active electrode and a return electrode that are positioned on the distal end of the electrosurgical instrument to treat the inner surface of the annulus fibrosus.
In yet another aspect, the present invention provides a method of treating an intervertebral disc. The method comprises positioning a distal end of an electrosurgical probe within close proximity of an outer surface of the intervertebral disc. A high frequency voltage is delivered between an active electrode and a return electrode. The high frequency voltage is sufficient to create a channel in the disc tissue. The active electrode is then advanced through the channel created in the intervertebral disc. The distal end of the electrosurgical instrument is moved to a curved configuration that approximates a curvature of an inner surface of the annulus fibrosus. A high frequency voltage is delivered between the active electrode and the return electrode to treat the inner surface of the annulus fibrosus.
In a further aspect, the present invention provides an apparatus for treating an intervertebral disc. The apparatus comprises a steerable distal end portion that is moveable to a curved configuration that approximates the curvature of the inner surface of an annulus fibrosus. At least one active electrode and a return electrode are positioned on the distal end of the apparatus. A high frequency energy source is configured to create a voltage difference between the active electrode and the return electrode. Preferably, the return electrode is positioned proximal of the active electrode so as to draw the electric current away from the target tissue.
In another aspect, the present invention provides a method of using an electrosurgical system for treating a disorder of an intervertebral disc of a patient, wherein the electrosurgical system includes a power supply coupled to at least one active electrode disposed on a shaft distal end of an electrosurgical probe. Such disc disorders include fragmentation and migration of the nucleus pulposus into the annulus fibrosus, discogenic or axial pain, one or more fissures in the annulus fibrosus, or contained herniation (a protrusion of the nucleus pulposus which is contained within the annulus fibrosus) of the disc. The method includes inserting the shaft distal end within the intervertebral disc such that the active electrode is in the vicinity of the tissue targeted for treatment (fissure, contained herniation, etc.), and thereafter applying a high frequency voltage between the active electrode and a return electrode sufficient to ablate target tissue. In preferred embodiments, the voltage generates a plasma in the vicinity of the target site and tissue at the target site is ablated by the molecular dissociation of disc tissue components to form low molecular weight ablation by-products, the latter being readily aspirated from the target site or tissue being treated.
In one embodiment, the shaft may be guided by a combination of axial translation of the shaft and rotation of the shaft about its longitudinal axis. In one aspect of the invention, the shaft has a pre-defined curvature, both before and after the shaft has been guided to the vicinity of the contained herniation. The pre-defined curvature may include a first and a second curve in the shaft, the second curve being proximal to the first curve.
In another aspect of the invention, the shaft may lack a pre-defined curvature, and may be bent to a suitable conformation prior to a particular surgical procedure. In yet another aspect of the invention, the shaft may lack a pre-defined curvature, and the shaft distal end may be steered during a surgical procedure so as to adopt a suitable conformation, thereby allowing the shaft distal end to be guided to a target site within an intervertebral disc.
By applying a high frequency voltage between the active electrode and the return electrode, disc tissue at the target site undergoes molecular dissociation. In one embodiment, the active electrode includes an electrode head having an apical spike and a cusp, wherein the electrode head is adapted for providing a high current density in the vicinity of the electrode head when a high frequency voltage is applied between the active electrode and the return electrode. The method may be conveniently performed percutaneously, and one or more stages in the treatment or procedure may be performed under fluoroscopy to allow visualization of the shaft within the disc to be treated.
Further aspects, features, and advantages of the present invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings.